The present invention relates to an electro-hydraulic arrangement for regulating a lifting mechanism on an agricultural working vehicle.
Arrangements of the above mentioned general type are known in the art. One of such arrangements is disclosed, for example, in the West German document DE-OS No. 2,508,620. In the arrangement disclosed in this document, the regulated magnitudes of position, pulling force and slippage are processed in a combined manner so as to provide in many applications of the tractor an elastic and fast operation of the regulating arrangement. Despite the fact that the processing of a slippage dependent signal is advantageous in many applications, this arrangement has the disadvantage that the main regulating magnitudes of the position and pulling force are not processed with one another in a mixing regulation. For both main regulating magnitudes, the regulating deviation is determined separately with aid of two nominal value transmitters and supplied via a switch to a non-linear unit with dead zone, whose output signal is first combined with the slippage dependent signal. In this arrangement the regulated magnitudes of position and slippage can also be combined with one another, which is undesirable in many applications. Instead of the mixing regulation, the switch performs, however, a switching between both main regulating magnitudes of position and pulling force. Moreover, in many cases the direct processing of the regulating magnitude of slippage is not advantageous. In the known regulating arrangement the slippage effect is supplied by a non-linear member for the regulation, and there is a limitation that the slippage effect acts only within a certain region. Also, its effect upon the regulating circuit is constant when the associated switch is closed.
Furthermore, an electro-hydraulic regulating arrangement for a tractor with an attached plow is known in which the pulling force regulating system is completed by a slippage feedback. In this arrangement a differential signal is produced from a nominal value and an actual value of the slippage and forms a slippage regulating deviation. This slippage regulating deviation is supplied to the nominal value of the pulling force so that the resulting nominal value signal of the pulling force is greater when the slippage regulating deviation is positive and smaller when it is negative. First the resulting nominal value signal of the pulling force is compared with the actual value signal of the pulling force and the resulting regulating deviation is produced, which is used for controlling lifting or lowering of the plow. In this type of combining the signals for slippage regulating deviation and nominal value of the pulling force, a resulting nominal value of the pulling force is produced which can be smaller or greater than the nominal value of the force. The resulting regulating deviation produced after the comparison with the actual value of the pulling force exceeds the region predetermined for it or does not fill the same. This can lead to unfavorable operation of the regulating device. Further, in this combination of the regulating magnitudes of slippage and pulling force, a high component of the slippage regulation is not realized since the nominal value of the pulling force is always in full strength to be added with the slippage regulating deviation. In many cases, however, a higher portion of slippage regulation is advantageous. A further disadvantage can also be in that with the position admixture, the slippage effect acts always in full magnitude over the nominal value. In this arrangement therefore a real mixing regulation is impossible. The use of two nominal value transmitters not only increases the expenses but also reduces the operator's comfort.